Athletes and active individuals have been identified as an at-risk group for a low vitamin D status, specifically those residing in countries of higher latitude (such as the United Kingdom). This especially applies to those who train indoors for their sport, this is because Vitamin D is primarily produced following skin exposure to ultraviolet B (UVB) exposure. Vitamin D is essential for the maintenance of optimal bone and musculoskeletal health. It has also been suggested to play a role in the prevention of illness incidence, such as in upper respiratory tract infections (URTI). More recent research has indicated that an improved Vitamin D status may also play a role in enhancing exercise performance. Therefore, having a poor vitamin D status could negatively impact athletic training and competition. The purpose of this study is to evaluate the prevalence of vitamin D deficiency in university athletes and inactive controls in spring and autumn.

During this study the subjects will be asked to visit the labs on two occasions, at the beginning of the study for baseline measurements, and again on two occasions at the end of the study. Participants will have the following outcomes assessed: Sport performance (vertical jump height, muscular strength and aerobic fitness), peripheral Quantitative Computed Tomography (pQCT) scan of the bone mineral composition of the tibia, total body composition via Dual Energy X-ray Absorptiometry (DEXA),total and hip/femoral head bone mineral density and content to assess fracture risk via DEXA. Serum 25(OH)D levels (≈15ml of whole blood will be collected for these measurements. Dietary intake using self-reported food diaries. In addition illness and injury incidence will be recorded daily throughout the study in a booklet provided to the participants.Throughout the trial, the participants will be contacted via telephone/ email on a monthly basis to discuss any issues and maintain good communication.

During this study the subjects will be asked to visit the labs on 4 different occasions. There will be two occasions, at the beginning of the study for baseline measurements, and again on two occasions at the end of the study.

Data collection will take place across two testing sessions (separated by ~24 - 72 hrs) in the Autumn and Spring period.

Session 1

• Peripheral Quantitative Computed Tomography (pQCT) scan of the bone mineral composition of the tibia.
• Total and percentage lean and fat mass and total bone mineral density via Dual Energy X-ray Absorptiometry (DEXA).
• Sport performance: Vertical jump height and maximal oxygen uptake (VO2 max) test.

Session 2

• Fasting serum 25(OH)D levels, lipid profile, glucose, insulin, serum calcium, albumin, parathyroid hormone, C- terminal telopeptide (CTX), full blood count, kidney, thyroid and liver function (≈15ml of whole blood will be collected for these measurements).
• Collection of self-reported food diaries to assess dietary intake
• Sport performance: muscular strength

Aerobic fitness will be tested using a VO2 max exercise protocol using a stationary cycle ergometer, the participants will be expected to perform this to maximal effort or exhaustion. The test will consist of progressive increments in cycling workload (power output, W) until volitional fatigue. The test will take about 8 - 12 minutes to complete and is dependent upon the fitness of the participants. This will take place in the Sport & Exercise Science laboratories based in the Clinical Investigation Unit (22AX00). All subjects will be supervised during exercise at all times and will implement an adequate warm-up and cool-down to minimize the risk of injury. Staff will be on hand throughout the testing trained adequately in basic life support (including defibrillation).

Muscular strength assessments will be performed at the Surrey Human Performance Institute. Muscular strength of the knee extensor and handgrip muscles will be determined using an Isokinetic Dynamometer and a handgrip dynamometer respectively. For each assessment three maximal effort isometric contractions will be performed and peak torque (nM) and strength (kg) will be recorded. Muscular power will be assessed through performance of a countermovement jump (CMJ).

Body composition (absolute and relative amount of lean and fat mass), whole body bone mineral density and hip and femur bone mineral density will be measured with the use of DEXA (located in the Sport & Exercise Science laboratories based in the Clinical Investigation Unit). Two scans will be performed: one for the assessment of whole body bone mineral density and body composition, and the other scan is performed to specifically assess fracture risk by scanning the hip and femoral head. Effective exposure doses for these scans are ~8uSv and ~4uSv respectively. The total effective dose is depending on the size ('thickness' & height) of the volunteer and is approximately equivalent to the cosmic radiation exposure received in 45min of a transatlantic flight, or the radiation dose received on eating 80g of Brazil nuts (Health Protection Agency).

Bone mineral content of the tibia will be assessed using pQCT and this will be correlated to bone mineral density data obtained from DEXA. One scan will be performed and effective exposure doses will be between 1.5-1.8uSv which is comparable to 10 min on a transatlantic flight or one handful of Brazil nuts. The estimated total exposure dose for a single subject during the entire study is ~28uSv which is the same level of exposure as an average UK citizen is exposed to over the course of 4 days via background radiation.

Results of the body composition, bone mineral density, jump height, muscular strength, aerobic fitness (maximal oxygen uptake: VO2max) and dietary intake from the self-reported food diaries will be made available to the subjects upon request. The results from the blood analysis will be reported to the subject if there are any health concerns raised. If the results are within healthy ranges the participants will not be contacted unless specifically requested for this information. The investigators will not be contacting their GPs if there are any concerns raised in the study however it will be stressed that participants should contact a GP to discuss the results found.

Upon commencing the study, the participants will be required to track their incidence of illness and training habits during the 20-week experimental period between baseline and conclusion measurements. Throughout this period the incidence of illness and days trained during the months must be recorded in a check-list booklet, which will be provided. An email reminder will be sent to prompt all participants to complete these booklets on a daily basis during the experimental period, this should only take 1-2 minutes every evening. Throughout the duration of the trial, the participants will be contacted via telephone/ email on a monthly basis to discuss any issues and maintain good communication.

Inclusion Criteria:

University athlete inclusion criteria:

• Male or female
• Aged 18-30
• Regularly train/compete for Team Surrey Basketball, Boat Club, Swimming and Waterpolo, Netball or Rugby (for more than 4 hours/week)
• In good physical health
• Have a BMI >18 kg/m2
• Able to provide written informed consent

Control group inclusion criteria:

• Male or Female
• Age 18-30
• Do not use sun beds/ will not be going on a sun holiday/ returning home to a traditional sun holiday location between February 2017 and October 2017. This is because the results will be used to represent the Vitamin D status of young sporting individuals residing within the UK during these seasons.
• Do not take supplements containing Vitamin D
• Do not compete for Team Surrey and exercise less than 150 minutes / week.
• BMI: 18 - 30 kg/m2

Exclusion Criteria:

• Currently receiving treatment for medical conditions that are likely to affect vitamin D metabolism
• Hypercalcaemia (>2.5mmol/L)
• Regular use of sun-beds
• Having a sun holiday one month prior to commencing the study or plans for a sun holiday within the study period or will be returning home to a sun holiday location.
• Use of vitamin supplements containing vitamin D (if the prospective participants agrees to stop Vitamin D supplementation to join the study, a wash-out period of 8 weeks prior to commencing the trial would be acceptable).
• Excess alcohol intake for participants aged 18 years (> 21 units for males, > 14 units for females per week, as per Government guidelines)
• Those under dietary restriction (except vegetarianism) or following a weight-reducing diet.
• Clinically significant haematological abnormalities other than mild anaemia (Hb <12.0g/dl)
• Active malignancy
• Pregnant or planning a pregnancy during the study period

Participants will be recruited from the university population in Surrey during term-time